WASHINGTON (AP) — Three State Department officials resigned under pressure Wednesday, less than a day after a damning report blamed management failures for a lack of security at the U.S. diplomatic mission in Benghazi, Libya, where militants killed the U.S. ambassador and three other Americans on Sept. 11.

An administration official said Eric Boswell, the assistant secretary of state for diplomatic security, Charlene Lamb, the deputy assistant secretary responsible for embassy security, and an unnamed official with the Bureau of Near East Affairs, had stepped down. The official spoke on condition of anonymity because he wasn't authorized to discuss personnel matters publicly.

The report said poor leadership in both bureaus left the post underprotected.

"Systemic failures and leadership and management deficiencies at senior levels within two bureaus" resulted in a security level that was "inadequate for Benghazi and grossly inadequate to deal with the attack that took place," according to the report released late Tuesday by the independent Accountability Review Board.

The issue of security at the mission and the deaths of the Americans became a political hot potato with Republicans accusing the Obama administration, and especially U.N. Amassador Susan Rice of playing down the possibility it was a terrorist attacik. Eventually Rice was forced to withdraw her name from consideration to replace Hillary Rodham Clinton as secretary of state during President Barack Obama's second term.

Rice had appeared on numerous TV talk shows the Sunday after the attack and linked it to an anti-Islamic U.S. film. Those comments came after evidence already pointed to a distinct militant attack.

The review board was led by Thomas Pickering, a retired ambassador, and Mike Mullen, a retired admiral and former chairman of the Joint Chiefs of Staff. They testified in closed sessions before frustrated lawmakers on the House Foreign Affairs Committee and the Senate Foreign Relations Committee.

"My impression is the State Department clearly failed the Boy Scout motto of be prepared," said Sen. John Barrasso, a Republican.

"They failed to anticipate what was coming because of how bad the security risk already was there. ... They failed to connect the dots. They didn't have adequate security leading up to the attack and once the attack occurred, the security was woefully inadequate."

Rep. Adam Schiff, a member of the House intelligence committee, said security was "plainly inadequate, intelligence collection needs to be improved, and our reliance on local militias was sorely misplaced." Schiff, a Democrat, added that "these are not mistakes we can afford to make again."

The House committee chairman, Rep. Mike Rogers, a Republican, said the report laid bare "the massive failure of the State Department at all levels, including senior leadership, to take action to protect our government employees abroad," and complained that no one was being held accountable.

Rogers also said he was dissatisfied with the lack of progress in finding the attackers.

Lamb testified in October before the House Oversight and Government Reform Committee and defended the security measures.

"I made the best decisions I could with the information I had," Lamb said. "We had the correct number of assets in Benghazi at the time of 9/11."

She also told Rep. Dan Burton, a Republican, that she rejected requests for more security in Benghazi, instead training "local Libyans and army men" to provide security, a policy in force at U.S. diplomatic facilities around the world.

The classified testimony by Pickering and Mullen set the stage for public hearings Thursday with Deputy Secretary of State William Burns, who is in charge of policy, and Deputy Secretary of State Thomas Nides, who is in charge of management.

Clinton was to have appeared at Thursday's hearings, but canceled after fainting and sustaining a concussion last week while recovering from a stomach virus. Clinton is under doctors' orders to rest.

The board determined that no individual officials ignored or violated their duties and recommended no disciplinary action. But it also said poor performance by senior managers should be grounds for disciplinary recommendations in the future.

Senate Republicans and Democrats said they hoped Clinton would testify on the Hill even though she is planning to step down from her Cabinet post.

In a letter that accompanied the transmission of the report to Congress, Clinton thanked the board for its "clear-eyed, serious look at serious systemic challenges" and said she accepted all of its 29 recommendations to improve security at high-threat embassies and consulates.

She said the department had begun to put in place some of the recommendations. They include increasing by several hundred the number of Marine guards stationed at diplomatic missions throughout the world; relying less on local security forces for protection at embassies, consulates and other offices; and increasing hiring and deployment of highly trained Diplomatic Security agents at at-risk posts.

Clinton agreed with the panel's finding that Congress must fully fund the State Department's security initiatives. The panel found that budget constraints in the past had led some management officials to emphasize savings over security, including rejecting numerous requests from the Benghazi mission and the embassy in Tripoli for enhanced protection.

House and Senate negotiators on the pending defense bill agreed on Tuesday to fund another 1,000 Marines at embassy security worldwide.

The report singled out the Bureau of Diplomatic Security and the Bureau of Near East Affairs for criticism, saying there appeared to be a lack of cooperation and confusion over protection at the mission in Benghazi, a city in Eastern Libya that was relatively lawless after the revolution that toppled Libyan strongman Moammar Gadhafi.

But it appeared to break little new ground about the timeline of the Benghazi attack during which Libyan Ambassador Chris Stevens, information specialist Sean Smith and former Navy commandos Glen Doherty and Tyrone Woods — who were contractors working for the CIA — were killed. Stevens' slaying was the first of a U.S. ambassador since 1988.

The board determined that there had been no immediate, specific tactical warning of a potential attack on the 11th anniversary of Sept. 11, 2001. But the report said there had been several worrisome incidents before to the attack that should have set off warning bells.

Sen. Jim Inhofe, a Republican, emerging from the Senate briefing on the report, kept up the congressional criticism of Rice.

"Now we all know she had knowledge. She knew what the truth was. It was a cover-up," he said.

While criticizing State Department management in Washington along with the local militia force and contract guards that the mission depended on for protection, the report said U.S. personnel on the ground in Benghazi "performed with courage and readiness to risk their lives to protect their colleagues in a near-impossible situation."

It said the response by Diplomatic Security agents on the scene and CIA operatives at a nearby compound that later came under attack itself had been "timely and appropriate" and absolved the military from any blame. "There was simply not enough time for armed U.S. military assets to have made a difference," it said.